Orbital Engineering Mediated by Cation Conjugation in Luminescent Uranyl-Organic Hybrid Materials.

Abstract

A series of compounds of the form [HAr]2 [UO2 X4 ] is reported here, wherein Ar is systematically varied between pyridine (1-X), quinoline (2-X), acridine (3-X), 2,5-dimethylpyrazine (4-X), quinoxaline (5-X), and phenazine (6-X), and X=Cl or Br. With greater conjugation in the organic cation, a larger quenching in uranyl luminescence is observed in the solid state. Supporting our luminescence experiments with computation, we map out the potential energy diagrams for the singlet and triplet states of both the [HAr]+ cations and [UO2 Cl4 ]2- anion in the crystalline state, and of the assembly. The distinct energy transfer pathways in each compound are discussed.